Protective circuits for secondary battery packs

ABSTRACT

This invention discloses a charging/discharging protective circuit for a secondary battery pack, having an over-charging/discharging voltage comparator, a reference voltage source and a battery status decision circuit. There is also a sampling circuit having a sequential pulse generator for generating pulses for selecting one of the batteries in the battery pack for testing purposes. The pulse generator provides M-channel gating pulses to the selection circuit of the battery under test and provides sampling pulses to the over-charging/discharging voltage comparators. The reference voltage source has a regulated output circuit. This invention uses time division inspection methods to provide a cost-effective solution for inspecting batteries in a battery pack.

CROSS REFERENCE

This application claims priority from a Chinese patent applicationentitled “A Type of Charging/Discharging Protective Circuit forSecondary Battery Packs” filed on Dec. 7, 2005, having a ChineseApplication No. 200510022293.4. This application is incorporated hereinby reference.

FIELD OF INVENTION

This invention involves protective integrated circuits for secondarybatteries and, in particular, protective charging/discharging circuitsfor secondary battery packs.

BACKGROUND

In lithium ion batteries storing high density internal energy, excessiveaccumulation of internal heat while in the over-charged state coulddamage battery performance and life, and, in particular, may result in abattery explosion and even fire. Therefore, such lithium ion batteriesmust have a well-designed protective circuit to ensure safety during theover-charged/discharged states and to prevent performance deteriorationas well. Most of the available integrated circuits for protection oflithium ion battery packs (hereinafter IC) utilizes pure analoguecircuits. Different reference voltage source ICs produced with CMOStechnology using different doping concentrations are not completely thesame, and the thresholds for over-charging/discharging protection willvary within a certain range. A large number of divider (bleed) resistorscan be designed into the IC by the designer based on such variations.There are also a large number of regulation points (for adjustment ofvariations) that can be designed in to adjust the resistors. Both ofthese approaches allow it possible to adjust the divider (bleed)resistance during intermediate testing according to the desired voltageratio and after the wafer has been manufactured. As a result, theresistance may be kept basically constant to meet the use requirementsor specification. Normally, the IC has a number of variable resistors,comparator and reference voltage sources, occupying about 40% of the ICarea. The accuracy of such adjustment remains relatively low, and theprotective voltage threshold of each battery has to be correctedseparately. To ensure adequate accuracy, laser is adopted to adjust toaround 100 regulation points for 3˜4 batteries, thus increasingproduction cost accordingly. Therefore, it is desirable to have asimpler and more cost effective protective circuit for the charging anddischarging and inspection of battery packs.

SUMMARY OF THE INVENTION

The technical problem to be solved by this invention is to overcome thedefects of the present technology and propose a protective circuit oflow cost and high accuracy for charging and discharging of secondarybattery packs.

Briefly, for the charging and discharging protective circuit for thesecondary battery pack, the secondary battery pack may have multiples ofM batteries (where M is more than 2), where the protective circuitincluding charging/discharging voltage comparators, a reference voltagesource which provides comparative reference voltage, and a batterystatus decision circuit connected to the output of theover-charging/discharging voltage comparator. The output of the saidbattery status decision circuit is connected to the batterycharging/discharging control circuit, which controls the charging anddischarging of the batteries in the battery pack.

There is a sampling circuit for controlling the sampling of the voltagelevels of the batteries and having a sequential pulse generator, whichprovides M-channel gating pulses (or strobes) to the selection circuitof the battery under test and provides sampling pulses to theover-charging/discharging voltage comparator. The said M-channel gatingpulses connect sequentially the M batteries under test to thecomparative voltage inputs of the voltage comparator, respectively. Thesampling pulses allow the sending samples of the comparison results ofthe voltage comparator to the battery status decision circuit.

DESCRIPTION OF THE DRAWINGS

The following are further descriptions of the invention with referencesto figures and examples of their applications.

FIG. 1 is a method embodiment of this invention, showing a blockdiagram;

FIG. 2 is an embodiment of this invention, showing a sequential wavediagram for a 4-channel gating pulses (or strobes);

FIG. 3 is an embodiment of this invention, showing a one-channel gatingpulses and the corresponding sequential wave diagram for samplingpulses;

FIG. 4 is a method of this invention, showing the regulated outputcircuit diagram for the reference voltage source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technical problem to be solved by this invention is to overcome thedefects of the present technology and propose a protective circuit oflow cost and high accuracy for charging/discharging of secondary batterypacks. The technical problems in this invention can be solved in thefollowing manner.

For the charging/discharging protective circuit for a secondary batterypack, the secondary battery pack having multiples of M batteries (whereM is more than 2), the circuit including charging/discharging voltagecomparators, a reference voltage source which provides comparativereference voltage levels, and a battery status decision circuitconnected to the output of the voltage comparators. The output of thesaid battery status decision circuit is connected externally to thebattery charging/discharging control circuit for controlling thecharging and discharging of the batteries in the battery pack.

The protective charging/discharging circuit for a secondary battery packincludes the following:

a comparative voltage source for the voltage comparators; and

a sampling circuit for the battery voltage having a sequential pulsegenerator, which provides M-channel gating pulses (or strobes) to theselection circuit and provides sampling pulses to the voltagecomparators. The said M-channel gating pulses allow the connectingsequentially of the M batteries under test to the voltage comparators,respectively. The sampling pulses allow the sending of the comparisonresults of the voltage comparators to the battery status decisioncircuit.

A secondary battery pack is an energy-storage component with itsterminal voltage varying slowly during normal conditions, and itscharging/discharging process being a continuous and smooth process.Therefore, the comparative voltage of the over-charging/dischargingvoltage comparator is sampled intermittently, and the voltage of thebattery under test is inspected at set time intervals.

On the other hand, over-current and short-circuit conditions are abruptabnormalities and must be protected immediately. Therefore, comparativevoltage for the over-current and short-circuit inspection voltagecomparators are provided in a continuously on-line method. During othertime, when there is no inspection of the batteries under test, theentire circuitry remains in a hibernation state for the purpose ofreducing power consumption, except the continuously on-line monitoringfor over-current and short-circuit conditions.

Technical problems in this invention are further solved in the followingway:

The reference voltage source has a regulated output circuit foradjusting the protective circuit to be within specification aftermanufacturing.

In the regulated output circuit of the said reference voltage source, amulti-stage voltage divider is comprised of adjustable-ratio resistorsand fixed-ratio resistors providing stepwise adjusted resistance.

Both ends of the said serial adjustable-ratio resistors are pressurewelding points for probe test, across which are fuses that may melt whenover-voltage or over-current conditions occur.

The sequential pulse generator, including a square wave generator, acascaded oscillator, frequency divider, and amplifier, intermittentlyinspects the voltage of the battery under test at set time intervals.When the gating pulses of a channel are at the high level, thecorresponding terminal voltage of the battery under test will be sent tothe input of comparative voltage of the voltage comparator via the levelconversion circuit. M-channel sampling pulses, which are at the highlevel only during the intervals set for the high level, will send thecomparison results of the voltage comparators to the battery statusdecision circuit.

Technical problems in this invention are solved on the followingselective basis:

The said secondary battery pack is a lithium ion battery pack.

M is an integer between 2 and 8. For the preferred selection, M is 3 or4.

The level conversion circuit is a differential operational amplifier.

The reference voltage source is a current amplification circuit at zerotemperature shift and intermittent energy band. Variation of referenceoperating points due to load variation at output terminals can beseparated, and a stable reference comparative voltage can be provided.

The circuits may be either hybrid discrete digital/analogue circuits, orhybrid integrated digital and analogue circuits. Layout can be made forthe IC by using small line width.

In comparison with the technology available now, the present invention,the sampling circuits creates a time division inspection system suchthat the number of regulating points needed to create the protectionthreshold voltage for the calibrating of the protective circuit can beminimized and in the preferred embodiment is reduced to 6 regulatingpoints, thus minimizing the need for wafer testing, saving regulationtime, and test equipment cost. The adjustment step for the thresholdvoltage for over-charging protection can be as high as 3.3 mV, and thesystem regulation step, namely the step accuracy, can be 10 mV. Theprotection threshold for over-discharging, over-current and shortcircuit can reach an accuracy of 5%. Accuracy of time delays reaches30%, 50% better than the existing technology.

As shown in FIG. 1, for the charging/discharging protective circuit of abattery pack, the battery pack may comprise 4 cascaded lithium ionbatteries: E1, E2, E3 and E4. The protective circuit includes voltagecomparators B1, B2, B3 and B4 for detecting over-charging,over-discharging, over-current and short circuit. There is also areference voltage source 2, providing them with comparative referencevoltage levels respectively. There is also a battery status decisioncircuit 1 connected to the outputs of voltage comparators B1, B2, B3 andB4. The output of said battery status decision circuit 1 is connected toa control circuit for battery charging and discharging, which in oneembodiment can be the field effect transistor M1 and M2 and freewheelingdiode D1 and D2. The battery status decision circuit 1 includes four8-digit counters for over-charging/discharging delay, a 4-digit counterfor over-current delay and auxiliary circuits. As over-charging andover-discharging will not occur at the same time, sharing of a group ofcounters can save a number of elements.

There is a comparative voltage source, comprising of a selection circuit3 for selecting one of the batteries for testing E1˜E4 and a levelconversion circuit 4, which provides an interface between the selectioncircuit and voltage comparator B1 and B2. The said level conversioncircuit 4 with a 2-stage differential operational amplifier, adoptingcommon-source and common-grid output, can satisfy the need forbandwidth. It has a large amplification multiple, high common-moderejection ratio and low power consumption.

There is a sampling circuit for battery voltage, including a sequentialpulse generator 5, which provides 4-channel pulses to the selectioncircuit for the selection of a battery E1˜E4 and sampling pulses tovoltage comparator B1 and B2. The said 4-channel gating pulses allowsthe sequential connection of one of the batteries E1˜E4 to be under testby connecting the selected battery to comparative voltage inputterminals of the voltage comparators B1 and B2. Note that thecomparative voltages from the voltage comparators B1 and B2 aregenerated by the intermittent sampling method (from pulses generated bythe sampling circuit). On the other hand, the comparative voltage of theover-current and short-current detection voltage comparators B3 and B4are provided by a continuous online detection method. These comparativevoltage inputs are connected to the discharging loop. The said samplingpulses allow the sending of the comparison results from theover-charging/discharging voltage comparators to the battery statusdecision circuit.

In the preferred method, the battery inspection cycle is set at T=10 mS,namely, voltages of the batteries are inspected at 10 mS intervals.Furthermore, the width of gating pulses for the batteries under testE1˜E4 is set at Pu=200 μS, gating pulse interval between two adjacentbatteries at Pc=200 μS, and sampling pulse width of batteries under testE1˜E4 at Pd=¼, Pu=50 μS. They are set at ½˜¾ of the corresponding gatingpulses so as to avoid influence from level variation. The sequentialwaveform of 4-channel gating pulses, as well as the sequential waveformof one-channel gating pulses and the corresponding sampling pulses areshown in FIGS. 2 and 3. The upper waveform in FIG. 3 is a sequentialwaveform of one of the channels in providing gating pulses, while thelower waveform is a sequential waveform of the corresponding samplingpulses.

The reference voltage source 2 has a regulated output circuit 8, wherebythe series of adjustable-ratio resistors of stepwise adjusted valuesR1-1, R1-2, R1-3, R1-4, R1-5, R1-6 and R1-7 as well as fixed ratioresistors R2, R3 and R4 form a multi-stage voltage divider, and 6adjustment points are provided accordingly.

Both ends of said series of adjustable-ratio resistors R1-1˜R1-7 arepressure welding points P0˜P6 for probe test, across which are F0˜F5fuses, that can be broken when over-current or over-voltage conditionoccurs.

The sequential pulse generator 5 is a square wave generator including acascaded oscillator 6, a quad frequency divider and an amplifier 7, withoscillator generating a square wave signal at 20K frequency. When achannel of gating pulses is at a high level, the terminal voltage of thecorresponding battery under test is sent via a level conversion circuit4 to the comparative voltage inputs of over-charging/discharging voltagecomparators B1 and B2. On the other hand, the 4-channel sampling pulses,which are at a high level only during the period set for the high level,allow the sending of the comparison results of correspondingover-charging/discharging voltage comparators B1 and B2 to the batterystatus decision circuit 1.

The reference voltage source 2 has a current amplification circuit, zerotemperature shift and intermittent energy band, and its output voltageis 2.5V.

The protective circuit operates in the following way: the 4-channelgating pulses generated by sequential pulse generator 5 controls theselection circuit 3 to sequentially connect one of the batteries E1˜E4to the level conversion circuit 4. Relative voltage on both terminals ofthe selected battery is changed to absolute voltage with reference tothe ground, and is applied respectively to the voltage comparators B1and B2 for comparison with their respective reference voltages. Thecomparison result (compared levels) is sampled by sampling pulsesgenerated from the sequential pulse generator 5, and the sampled resultis sent to the battery status decision circuit 1. The battery statusdecision circuit 1 counts the continuously sampled result of the samebattery, and finally sends a corresponding control level to thecharging/discharging control circuit. Such control circuit may use fieldeffect transistor M1 and M2 as well as freewheeling diode D1 and D2. Thepurpose of the control circuit is to protect the battery pack fromabnormal battery conditions.

As shown in FIG. 4, in the regulated output circuit 8 of referencevoltage source 2, Vref 1 is the comparative reference voltage for theover-charging voltage comparators B1, Vref 2 is the comparativereference voltage for over-discharging voltage comparator B2 and shortcircuit detection voltage comparator B4, and Vref 3 is the comparativereference voltage for over-current detection voltage comparator B3. Thecharacteristics of the lithium battery themselves confine the protectivethreshold for over-charging normally to 4.2V˜4.4V. In case of anexcessively low threshold, the battery can not be fully charged, as itis placed under protection before the battery is fully charged. In caseof an excessively high threshold, there will be a risk of batteryexpansion and break and even explosion. In this specific implementationmethod, the voltage threshold for charging protection is madecontinuously adjustable in the range of 4.2V˜4.4V (center value 4.3V) byregulating adjustment resistor R1. Voltage threshold forover-discharging protection is around 2.5V, voltage threshold forover-current protection is around 0.3V, and voltage threshold for shortcircuit protection is around 1.25V. All the resistors in FIG. 4 areratio-resistors, with their resistance being given in the figures. R1 isin the range of 27.8 KΩ˜84.5 KΩ, continuously adjustable in steps of 0.9KΩ. Through adjustment of resistance of R1, the voltage threshold forover-charging protection is made continuously adjustable in the range of4.202V˜4.398V, with its maximal adjustment step being as small as 3.3mV. Considering differences in resistance as well as offset voltage ofthe level conversion circuit, the system adjustment step of the voltagethreshold for over-charging protection is made to be 10 mV throughemulation and calculation. In other words, the regulated voltagethreshold for IC over-charging protection can be continuously adjustablein the range of 4.2V˜4.4V, with the adjustment accuracy being ±10 mV ofthe set value. The variation range of the voltage thresholds forover-discharging protection, short circuit protection and over currentprotection can be determined on the basis of the range of voltagethreshold for over-charging protection. Considering etching accuracy ofthe resistors, uneven doping concentration, the nominal range of thevariation of voltage thresholds for over-discharging protection, shortcircuit protection and over current protection is set at 5%. All ratioresistors are in the form of cascaded and parallel resistor units ofequal length and width, and pseudo resistors are added on both sides toreduce environmental impact and strengthen consistency of resistancevalues.

The above content is a further detailed description of this invention incombination with specific selective implementation methods, and thespecific implementation of this invention can not be considered to beconfined to such descriptions. Ordinary technicians, working in thefiled of technology of this invention, can make some simple inferencesor substitutions under the prerequisite of not departing from theconception of this invention. Such inferences or substitutions shouldall be deemed to fall in the range of patent protection as determined inthe claims submitted for this invention.

1. A protective circuit for a secondary battery pack having a pluralityof batteries, comprising: a sampling circuit generating pulses forselecting one or more of the batteries for inspection; a selectioncircuit for receiving said pulses and selecting a battery in the batterypack; a reference voltage source providing one or more reference levels,wherein the reference voltage source has a regulated output circuit thatcalibrates protection threshold voltages of the protective circuit; fouror more voltage comparators each receiving one of the reference levelsto compare with the level of the selected battery and generating one ormore compared levels, wherein a first comparator detects over-chargingof said batteries, a second comparator detects over-discharging of saidbatteries, a third comparator detects over-current through saidbatteries, and a fourth comparator detects a short circuit of saidbatteries, wherein the reference levels comprise, a first referencevoltage, a second reference voltage, and a third reference voltage, andwherein the first reference voltage is input for said first comparator,the second reference voltage is input for said second comparator and forsaid fourth comparator, and the third reference voltage is input forsaid third comparator; battery status decision circuit connected to thecomparators generating control signals as a function of the comparedlevels; and battery charging/discharging control circuit for controllingthe charging or discharging of the selected battery in response to thecontrol signals.
 2. The protective circuit of claim 1 wherein in theregulated output circuit, there is a multi-stage voltage divider withadjustable-ratio resistors and fixed-ratio resistors providing stepwiseadjusted resistance to adjust the reference levels for calibrating theprotective circuit to be within predetermined inspection ranges.
 3. Theprotective circuit of claim 1 wherein the sampling circuit includes asequential pulse generator.
 4. The protective circuit of claim 1 whereinthe sampling circuit includes a sequential pulse generator generatingpulses for the inspecting the batteries at predetermined time intervals.5. The protective circuit of claim 3 wherein the sampling circuitfarther includes a square wave generator, cascaded oscillator, frequencydivider and amplifier.
 6. The protective circuit of claim 1 wherein thesampling circuit causes the intermittently inspection the voltages ofthe batteries at set time intervals.
 7. The protective circuit of claim1 wherein the batteries of the secondary battery pack are lithium ionbatteries.
 8. The protective circuit of claim 1 wherein the battery packis configured in multiples of M batteries where M is an integer between2 and
 8. 9. The protective circuit of claim 1 further including a levelconversion circuit connected between the selection circuit and thecomparators.
 10. The protective circuit of claim 9 wherein the levelconversion circuit is a differential operational amplifier.
 11. Theprotective circuit of claim 1 the protective circuit is a discretehybrid digital/analogue circuit.
 12. The protective circuit of claim 1the protective circuit is a hybrid integrated digital/analogue circuit.13. The protective circuit of claim 2 wherein for the multi-stagevoltage divider, the adjustable-ratio resistors and the fixed ratioresistors are connected in series, and wherein the two ends of each ofthe adjustable-ratio resistors are connected by a fuse for adjusting thecombined resistance of the adjustable resistors.
 14. A protectivecircuit for a secondary battery pack having a plurality of batteries,comprising: a sampling circuit generating pulses for selecting one ormore of the batteries for inspection, wherein the sampling circuitincludes a sequential pulse generator generating pulses for inspectingselected one of the batteries at predetermined time intervals; aselection circuit receiving the pulses and for selecting a battery inthe battery pack; a reference voltage source providing one or morereference levels, wherein the reference voltage source has a regulatedoutput circuit that adjusts the reference levels in the calibration ofthe protective circuit; four or more voltage comparators each receivingone of the reference levels to compare with the level of the selectedbattery and generating one or more compared levels, wherein a firstcomparator detects over-charging of said batteries, a second comparatordetects over-discharging of said batteries, a third comparator detectsover-current through said batteries, and a fourth comparator detects ashort circuit of said batteries, wherein the reference levels comprise,a first reference voltage, a second reference voltage, and a thirdreference voltage, and wherein the first reference voltage is input forsaid first comparator, the second reference voltage is input for saidsecond comparator and for said fourth comparator, and the thirdreference voltage is input for said third comparator; a battery statusdecision circuit connected to the comparators generating control signalsas a function of the compared levels; and a battery charging/dischargingcontrol circuit for controlling the charging or discharging of theselected battery in response to the control signals.
 15. The protectivecircuit of claim 14 wherein in the regulated output circuit, there is amulti-stage voltage divider with adjustable-ratio resistors andfixed-ratio resistors providing stepwise adjusted resistance to adjustthe reference levels for calibrating the protective circuit to be withinpredetermined inspection ranges, wherein for the multi-stage voltagedivider, the adjustable-ratio resistors and the fixed ratio resistorsare connected in series, and wherein the two ends of each of theadjustable-ratio resistors are connected by a fuse for adjusting thecombined resistance of the adjustable resistors.
 16. The protectivecircuit of claim 14 wherein the batteries of the secondary battery packare lithium ion batteries.
 17. The protective circuit of claim 14wherein the battery pack is configured in multiples of M batteries whereM is an integer between 2 and
 8. 18. The protective circuit of claim 14further including a level conversion circuit connected between theselection circuit and the comparators.
 19. The protective circuit ofclaim 14 the protective circuit is a discrete hybrid digital/analoguecircuit.
 20. The protective circuit of claim 14 the protective circuitis a hybrid integrated digital/analogue circuit.